Selection of High Affinity Peptides Against Hepatitis B Core Antigen from a Phage-Displayed Cyclic Peptide Library

Ho, Kok Lian (2002) Selection of High Affinity Peptides Against Hepatitis B Core Antigen from a Phage-Displayed Cyclic Peptide Library. Masters thesis, Universiti Pertanian Malaysia.

[img] PDF
1201Kb

Abstract

Hepatitis B virus is the prototype member of the family Hepadnaviridae which causes acute and chronic liver diseases worldwide. The viral nucleocapsid containing a partially double stranded DNA is surrounded by an envelope comprises three distinct but related surface proteins (HBsAg), termed as small (S), medium (M) and large (L)-HBsAg. The essential subunit of the nucleocapsid is a polypeptide comprising 183 amino acids known as core protein (HBcAg). HBcAg produced in Escherichia coli is capable of self-assembly into core-like particles and can be purified easily with ammonium sulphate precipitation and sucrose gradient centrifugation. Core particles make of full-length HB cAg were used as substrate in biopanning with a cysteine constrained phage-displayed heptapeptide library. The most frequently identified phage clones displayed the cyclic peptides C-WSFFS NI-C and C-WPFWGPW-C. The relative dissociation constant (Krl) values for the interaction between the p hages and HBcAg were determined by an equilibrium binding assay in solution. The Kiel values for phage bearing peptides C-WSFFSNI-C and C-WPFWGPW-C for full-length and truncated HBcAg are less than 10 and 30 nM, respectively, which are 17- and 7- fold stronger than that of phage bearing the l inear peptide LLGRMK. The selected phages were able to compete with monoclonal antibody C 1-5 for a binding site on the surface of core particles, suggesting that the docking site of these phages may partially overlap with the epitope of mAb C 1-5, which was mapped at amino acid positions 78 to 83 at the tips of the core particles. The heavy chain of mAb C l-5 is hydrophobic and was proposed to be the contact region for HBcAg. Interestingly, the isolated peptides C-WSFFS NI-C and C-WPFWGPW-C are mainly composed of hydrophobic amino acids and may bind to the same region as mAb C l-5. A synthetic linear peptide bearing the sequence WSFFSNI inhibited the binding of L-HBsAg to core particles in vitro with an inhibition concentration (IC₅₀) approximately 9.8 µM. The additional of cysteine residues to both the N- and C-termini of the peptide greatly reduced the solubility of this cyclic peptide, and as a result the IC₅₀ is approximately 20-fold higher than that of WSFFSNI. A suitable recombinant carrier therefore is needed in order to reduce the hydrophobicity of the peptides and subsequently acts as a deli very system for targeting the peptide to virally infected cells.

Item Type:Thesis (Masters)
Subject:Peptides
Subject:Hepatitis B virus
Chairman Supervisor:Dr. Tan Wen Siang, PhD
Call Number:FSAS 2002 15
Faculty or Institute:Faculty of Science and Environmental Studies
ID Code:9380
Deposited By: Tuan Norasiah Tuan Yaacob
Deposited On:27 Jan 2011 10:19
Last Modified:30 Sep 2013 08:49

Repository Staff Only: item control page


Universiti Putra Malaysia Institutional Repository

Universiti Putra Malaysia Institutional Repository is an on-line digital archive that serves as a central collection and storage of scientific information and research at the Universiti Putra Malaysia.

Currently, the collections deposited in the IR consists of Master and PhD theses, Master and PhD Project Report, Journal Articles, Journal Bulletins, Conference Papers, UPM News, Newspaper Cuttings, Patents and Inaugural Lectures.

As the policy of the university does not permit users to view thesis in full text, access is only given to the first 24 pages only.